Anti-lock brake systems include solenoid-actuated relief valves that relieve the hydraulic pressure applied to the brakes when the wheels start to skid, i.e., to lock. By relieving the hydraulic braking pressure, the wheels are permitted to roll while nonetheless being slowed by the brakes, which significantly promotes control of the vehicle relative to what is experienced when the brakes lock.
Typically, an anti-lock relief valve includes a ball that is attached to a solenoid plunger. The relief valve also includes a valve seat that receives the ball. To relieve pressure in the hydraulic lines, the solenoid is actuated to move the ball away from the seat, thereby opening a relief passageway through which hydraulic fluid can flow back to a brake fluid reservoir.
The rate of hydraulic fluid flow through the relief passageway must be established to be sufficiently high to quickly alleviate skidding, but not so high as to cease braking altogether or to cause braking instability. Because the relief passageway itself must be kept sufficiently large to provide an adequate seating surface for the ball at one end of the passageway, conventional relief valves establish the rate of fluid flow by press-fitting an orifice cup into the relief passageway, with the orifice cup being formed with an orifice that is configured to establish the desired fluid flow rate.
As recognized herein, however, several disadvantages attend the use of orifice cups. For example, the orifice cup can be unintentionally deformed during the press-fitting process, degrading the performance of the cup. Furthermore, contaminants can enter the hydraulic system during press-fitting. Moreover, occasionally hydraulic fluid can leak between the sides of the orifice cup and the passageway into which it is press-fit. Still further, once installed only the size of the orifice can be easily inspected, not the entire cup. And, the press-fit process is difficult to monitor for installation errors. Apart from the above problems, requiring an orifice cup that is separate from the valve body adds to the number of components and, hence, to the cost of the relief valve. Having recognized these drawbacks, the present invention has provided the below-disclosed solutions to one or more of the prior art deficiencies.